The introduction of high external loads into the fuselage structure of an aircraft involves complex structural design requirements and intensive weight requirements. Until now, two variants have been used for the connection in aircraft construction. Such forms of load occur, for example, at the undercarriage during the takeoff or landing of an aircraft.
In the case of a first variant, a fork-shaped fitting with a base plate is screwed or riveted through the skin of the fuselage cell to an interior frame. It is of disadvantage in the case of this embodiment that the frame flanges are subjected to flexural loading and this increased stress has to be taken into consideration in the dimensioning. In addition, the frame flange must be of a width that corresponds to a width of the base plate of the fork fitting, at least in the connecting region. Since the introduction of the loads takes place in a punctiform manner, both the skin of the fuselage cell and the frame must be locally reinforced, which is very difficult in terms of structural design, specifically in the case of the skin of the fuselage cell. The overall effect of the influencing factors mentioned is that of increasing the weight.
In the case of a second variant, frames are used for the force introduction, the fork fitting being an integral part of the frame itself. This form of construction requires wide frames in the connecting region, since on the one hand the width of the frame must correspond to the width of the fork fitting and on the other hand the external loads in the edge region of the integrally formed fork fitting are transferred into the skin of the fuselage cell. A further difficulty is that this cutout in the skin of the fuselage cell, which is already large in any case, requires a second-row, pressure-tight riveting. Both aspects have a weight-increasing effect. In addition, the production of the fork fittings formed integrally with the frame is found to be very complex in production engineering terms.